1. Field of the Invention
The present invention relates to a switch actuation device that turns on and off a switch in accordance with movement or rotation of plural movable members, and an interlock mechanism and an image forming apparatus, such as a copier, a facsimile apparatus, a printer, etc., incorporating the switch actuation device.
2. Description of the Background Art
A conventional interlock mechanism includes a switch that operates in accordance with opening and closing of a wall cover constituting a housing of an electronic instrument is known. Also known is that power supply and general control are stopped when the wall cover is opened and the switch is turned off.
Such an interlock mechanism is also employed in an image forming apparatus, such as a copier, a facsimile apparatus, a printer, etc. For example, an interlock mechanism is used to control a switch actuation device to turn off a switch and stop supplying power in an image forming apparatus when a part of an openably closable housing is opened during maintenance, such as removing a jammed sheet, replenishing toner, replacing a process unit with a new one, etc. When an image forming apparatus includes plural openably closable covers, plural switch actuation devices are sometimes employed corresponding thereto to maintain the image forming apparatus by opening and closing one of the plural covers. However, a number of switch actuation devices increases as a result.
Japanese Patent Application Laid Open No. H05-165267 (JP-H05-165267-A) describes an image forming apparatus that includes an actuation lever that moves to an actuation position to actuate a switch in accordance with opening and closing of a first cover, and a movable lever that moves the actuation lever to the actuation position to actuate the switch in accordance with opening and closing of a second cover. Consequently, by combining the first actuation lever with the second movable lever, a power supply can be turned on and off in accordance with opening and closing of plural covers.
However, in the image forming apparatus of the JP-H05-165267-A, due to fluctuation in positions or shapes of a pressing member provided on a cover to press and activate the actuation and movable levers or of the levers themselves, the switch does not operate sometimes even when the cover is closed. Otherwise, the switch is possibly damaged or deformed when the cover is closed and the actuation lever excessively presses the actuation lever simultaneously.
Japanese Patent Application Laid Open No. 2008-37054 (JP-2008-37054-A) describes an interlock mechanism that employs a switch turned on when a switch actuation element is internally depressed against a bias force of a spring provided inside a switch housing. Such an interlock mechanism employs plural members to differentiate a direction in which a switch actuation element is turned on from that in which an openably closable cover moves when being closed. Owing to such a configuration of the differentiation mechanism, a force of a cover is indirectly conveyed to the switch actuation element and is not directly conveyed to the switch actuation element from the cover. Accordingly, the switch can avoid damage, even when subjected to a force more powerful than expected when the cover is closed.
However, the switch is overloaded depending on fluctuation in positions of a pressing member pressing the switch actuation element and shapes thereof in the interlock mechanism of JP-2008-37054-A.
As a configuration capable of obtaining stable actuation regardless of fluctuation in closing and opening and movement amounts of plural covers, Japanese Patent Application Laid-Open No. 2009-37997(JP-2009-37997-A) proposes a switch actuation device that includes a first swingable lever and a second lever pivotally supported by a support shaft provided on the first lever serving as a fulcrum at its middle portion with its one end facing the switch. The switch actuation device further includes a first actuation section that causes a second lever to swing toward a switch in accordance with opening and closing of one of two openably closable covers. Further included is a second actuation section that causes the first lever to swing in accordance with opening and closing of the other one of the two openably closable covers. Thus, when the other one of the two openably closable cover is closed, the second actuation section swings the first lever and causes the second lever to approach an actuator of a switch. Further, when one of the two openably closable covers is closed, the first actuation section makes one of swinging ends of the second lever to swing toward an actuator of a switch, and causes one of swinging ends of the second lever to press and move the actuator, and turn on the switch. With such a switch actuation device, even when amounts of opening and closing and movement fluctuate, a mutual positional relation between the first and second actuation sections and the first and second levers can be stably maintained by forming the first and second actuation sections in a cam shape. As a result, contact positions between the first and second actuation sections and the first and second levers can be substantially the same, respectively, so that a stable operation can be obtained.
However, in the switch actuation device of JP-2009-37997-A, depending on and owing to fluctuation in positions and shapes of the second lever that directly contacts the switch, the switch is susceptible to being, overloaded.